Alex and Daniel

We checked a Noliac NAC2125-H08 for shorts and found none. We measured the capacitance to be 2.4641 uF. The expected capacitance is 2.4 uF. We also measured a resistance of 3.5082 kOhm. When we pressed on the piezo, we noticed a voltage. We flagged one of the wires for polairty. See attached photos. We also noticed that the nylon tipped set screws that hold the piezo in place provide a voltage.

I 3D printed a holder for the Covesion SHG and its fibers. 

I looed at the crusher mirror to see if there was any damage. The backside had a ring with the outline of the nub, but the front did not have any damage I could see. The plate was also indented with the AJS Screw. See attached photos.

I tested the voltage across a Noliac 2023-H08-A01 and Thorlabs PA44M3KW. When measuring the voltage accross the positive lead, there is a positive voltage under compression. For Noliac piezos, the positive lead has a black dot next to it. We should flag this positive lead as this one is. See attached photos.

.jpeg files are now image files and display. I may have accidentally removed previous .jpeg files. 

I added back all my .jpeg files, and most other image files are .png

I cleaned the exterior of the following parts for the Laser Filter Cavity (LFC) using isopropanol and Kim wipes. Some tape and tape residue remains, so a more aggressive cleaning agent might be required before we bring the parts into B102 to clean the insides. See attached photos for the parts I cleaned.

Parts cleaned for LFC:

8" to 6" reducing Tee, 12" Long

6" Gate Valve (quantity 2)

End Cube and End Cube Base (quantity 2)

8" diameter bellows, 5" long (probably needs more clenaing before we bring it to B102)

Long 10" to 8" Reducer "flange"

Short 10" to 8" Reducer flange

Misc 10" Flanges

I also cleaned the following parts attached to the above parts that are not needed for the LFC:

An additional 8" to 6" reducing Tee, 12" Long

6" diameter flange, 12" long tube (quantity 2)

Following the simulation in (https://mccullerlab.com/logs/lab/index.php?callRep=11455), I decided to use an optic with a constant thickness and material, instead of the substrate having the same thickness. Thus, the whole optic (coating+substrate+coating) is 2 mm thick. For the thick coating, each layer is 100 um. For the thin coating, each layer is 20 um. Interestingly, the location of the peaks changes even though the entire optic is the same thickness. This suggests the loss angle affects the eigenfrequencies, at least in the COMSOL model.

Having any BNC plugged into the DC modulation port of the thorlabs laser turnkey raising a forest of 840 Hz lines and its multiples in the noise spectra. Lee suggests it a grounding error in the input port and can be fixed with instrumentation amplifier between the signal and the port. 

[Daniel, Torrey]

Tried locking the filter cavity with and without the high voltage amplifier. This can be done by scanning on the laser frequency instead of the piezo, while still locking with piezo. From 11454 you can see the 3db roll off point is ~10 kHz. IMG_0068.png shows that the amplitudes to not differ until this point, at which point the cavity lock with the HV amplifier in place rolls off in amplitude much faster. Additionally the phase is much better with no HV amplifier.

I repeated the simulation from https://mccullerlab.com/logs/lab/index.php?callRep=11445 but with a coating thickness of 40 um instead of 20 um. I doubled the amount of mesh elements in the coating so that the mesh density of the coating remained the same. The PSD in the coating at 12.5 MHz and 13 MHz, which are roughly centered between the peaks, are 2.3x higher and 3.38x higher, respectivly. The eigenfrequency of the bulk longitudinal mode is lower since the optic is 1% thicker. For the simplest test of how the total loss angle gets calculated, I am going to go back to a low Q silicon coating.

Quick data dump in case this is needed in the future.

See attached photos for some photos of the Laser Filter Cavity SolidWorks Assembly

[Daniel, Torrey]

We tested an alternate way to hold the piezo in place for the cavity. We glued a mirror to a piezo to a 1/4" thick, 1" diameter spacer (the spacer is required to hold the assembly, the thorlabs piezo is too small). The spacer is then held in place by 3 set screws with nylon tips. See pics below. After realigning the cavity we noticed the quality of the lock is arguably worse (the alignment was much farther off compared to just replacing the piezo). Additionally, the 3.3 kHz resonance is more pronounced. 

In the previous set up, where the SM1 ring and viton o-ring are used to tighten, we found some metal shavings on the viton o-ring. Potentially concerning down the road. 

[Daniel, Torrey]

We've been running a test for a few weeks tracking the efficiency of the power distribution center. In the current configuration, it is possible to get the efficiency of the fiber collimator + fibers to high 80 percents. It should be noted as well that there were large temperature changes in the first three days of this data.

The MISC path is a standard 2 axis tip tilt mount compared to the other 3 paths which are the 5 degrees of freedom mounts. The initial theory was there is a relaxation time to some of these mounts on a several day time scale leading to loss of power in the 5 DOF mount. But this suggests something drifting upstream to me.

Attached are descriptions of the measurement setup used in log post 11449, as well as transfer function and noise data.

The piezo used here was Thorlabs, as described in 11449. The piezo transfer functions taken in log post 11373 were of the Noliac, would it be useful to take the same measurement of the Thorlabs piezo? Should it give us the same transfer function we will get by quotienting the open loop transfer function by the controller?

The noise measurements were taken with the laser locked, with the fan off and fan on.

Continuation of 11447.

Attached are several different OLG measurements with the cavity locked. The differences are as follows:

Thorlabspiezo-differentsm1tightness.png is the thorlabs piezo on both traces, without adjusting the controller shape. The active trace is screwing in the SM1 ring a fair amount, almost no slack left.

noliacpiezodifferentsm1tighness.png is the Noliac piezo on both traces. Additionally without changing the loop shape (between the two measurements, but changed from piezo to piezo). The active trace is again screwing in the SM1 ring a good amount.

Differentpiezos.png is a comparison of the two piezos with the same loop shape. Note the large difference in UGF.

Take aways:

1) Tightening the SM1 ring doesn't seem to effect the OLG when using the thorlabs piezo. Therefore I'm not sure its worth testing the stiffnesses of the o-rings used in the set up for the thorlabs piezo. For the noliac, it does seem to flatten some lower frequency parts of the OLG. It also lowered the UGF.

2) The 3.3 kHz mystery feature is in the transfer function of both piezos. If this feature is eliminated, I think the thorlabs piezo could become sufficient for locking these cavities with a mirror.

I think we should buy some more of the thorlabs piezos at different sizes, as they are relatively cheap, and test them on this cavity. 

[Daniel, Torrey]

We replaced the Noliac NAC2125-H08 piezo with a Thorlabs PA44M3KW to see if it changed the UGF. Everything else stayed the same physically, the control loop of the slow controller was shaped to optimize lock quality. The UGF went from 1 kHz to 3.5 kHz. Visibily the lock seems much more stable. I think it is worth testing difference stiffnesses of the viton o-rings in the piezo mirror set ups (the piezo pushes into the viton o-ring to change the length of the cavity). 

Take the custom made square aluminum base with four 1/4-20 holes, screw in an SM1 ring, then add a viton o-ring and mirror face down. With the custom made top, which looks like two concentric cylinders with a slot, add 3 #4 nylon tipped set screws. Add a tested piezo (see the previous piezo testing posts) with the wires through the slot. Center the piezo by gently tightening the set screws. Take the piezo base and back off the mirror so that it is under the top face. Add the top with the piezo to the base, and insert and fully tighten the 1/4-20 screws. Hold the assembly upright gently screw in the sm1 ring until you feel some resistance due to the piezo interfacing with the mirror. Then back off the set screws that hold the piezo.

<I will add photos the next time I do this procedure>